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The Caribbean through-flow (CTF) is a vital component of Earth’s climate system, facilitating and impacted by heat and salt fluxes from major circulation systems like the North Atlantic Subtropical Gyre (NASTG) and Atlantic Meridional Overturning Circulation (AMOC). Here, we show significant changes have occurred in upper ocean water mass properties of the CTF since 1960, including subsurface warming of ~ 0.2 °C decade−1, surface freshening of ~ 0.13 g kg−1 decade−1, and subsurface salinification of ~ 0.05 g kg−1 decade−1. In the upper 0–200 m, temperature and stability increases are nearly 3 and 20 times larger than globally averaged trends, respectively, with implications for tropical cyclones, sea level rise, and marine ecosystems. We show these upper ocean changes are likely impacting water mass formation in the NASTG, thereby indirectly influencing the AMOC. These findings highlight the CTF as a bottleneck for climatically important water masses and emphasize the need for sustained subsurface observations here. 

Abstract Few observational platforms are able to sustain direct measurements of all the key variables needed in the bulk calculation of air‐sea carbon dioxide (CO₂) exchange, a capability newly established for some Uncrewed Surface Vehicles (USVs). Western boundary currents are particularly challenging observational regions due to strong variability and dangerous sea states but are also known hot spots for CO₂uptake, making air‐sea exchange quantification in this region both difficult and important. Here, we present new observations collected by Saildrone USVs in the Gulf Stream during the winters of 2019 and 2022. We compared Saildrone data across co‐located vehicles and against the Pioneer Array moorings to validate the data quality. We explored how CO₂flux estimates differ when all variables needed to calculate fluxes from the bulk formulas are simultaneously measured on the same platform, relative to the situation where in situ observations must be combined with publicly‐available data products. We systematically replaced variables in the bulk formula with those often used for local and regional flux estimates. The analysis revealed that when using the ERA‐5 reanalysis wind speed in place of in situ observations, the ocean uptake of CO₂is underestimated by 8%; this underestimate grows to 9% if the NOAA Marine Boundary Layer atmospheric CO₂product and ERA‐5 significant wave height are also used in place of in situ observations. Overall our findings point to the importance of collecting contemporaneous observations of wind speed and oceanpCO₂to reduce biases in estimates of regional CO₂flux, especially during high wind events. 

Abstract A simplifying assumption in many studies of ocean carbon uptake is that the atmosphere is well‐mixed, such that zonal variations in its carbon dioxide (CO₂) content can be neglected in the calculation of air‐sea fluxes. Here, we examine this assumption at various scales to quantify the errors it introduces. For global annual averages, we find that positive and negative errors effectively cancel, so the use of atmospheric zonal‐average CO₂introduces reassuringly small errors in fluxes. However, for millions of square kilometers of the North Pacific and Atlantic that are downwind of the highly industrialized northern hemisphere continents, these biases average to over 6% of the annual ocean uptake and can cause errors of up to 30% on a given day. This work highlights the need to use a high quality, spatially‐resolved atmospheric CO₂product for process studies and for accurate long‐term average maps of ocean carbon uptake. 

Abstract The Observing Air–Sea Interactions Strategy (OASIS) is a new United Nations Decade of Ocean Science for Sustainable Development programme working to develop a practical, integrated approach for observing air–sea interactions globally for improved Earth system (including ecosystem) forecasts, CO2 uptake assessments called for by the Paris Agreement, and invaluable surface ocean information for decision makers. Our “Theory of Change” relies upon leveraged multi-disciplinary activities, partnerships, and capacity strengthening. Recommendations from >40 OceanObs’19 community papers and a series of workshops have been consolidated into three interlinked Grand Ideas for creating #1: a globally distributed network of mobile air–sea observing platforms built around an expanded array of long-term time-series stations; #2: a satellite network, with high spatial and temporal resolution, optimized for measuring air–sea fluxes; and #3: improved representation of air–sea coupling in a hierarchy of Earth system models. OASIS activities are organized across five Theme Teams: (1) Observing Network Design & Model Improvement; (2) Partnership & Capacity Strengthening; (3) UN Decade OASIS Actions; (4) Best Practices & Interoperability Experiments; and (5) Findable–Accessible–Interoperable–Reusable (FAIR) models, data, and OASIS products. Stakeholders, including researchers, are actively recruited to participate in Theme Teams to help promote a predicted, safe, clean, healthy, resilient, and productive ocean.